Open-Wrt: Add static library

In this section, you are going to learn

What is static library ?

How to create a static library in Open-WRT ?

How to link static library with object files for RPI-4B ?

How to flash full openwrt image for RPI-4B ?

How to run minicom and work remotely with RPI-4B ?

Topics in this section,

PART A: CREATING STATIC LIBRARY

• Step 1: Add custom application

  • Step 1.1: Add directory structure of “Static Library” application package

  • Step 1.2: Create directory under package/libs directory

  • Step 1.3: Create directories under my_static_lib directory

  • Step 1.4: Create my_static_lib.c under src directory

  • Step 1.5: Create my_static_lib.h under inc directory

  • Step 1.6: Create Makefile in “my_static_lib” directory

  • Step 1.7: Explanation of Makefile part by part

• Step 2 : Add application package to menuconfig

  • Step 2.1: Create feeds.conf file

  • Step 2.2: Content of feeds.conf

  • Step 2.3: Below example for feeds path

• Step 3 : Update and install feeds

  • Step 3.1: Commands for update and install feeds

• Step 4 : Enable application package in menuconfig

  • Step 4.1: Select your application in menuconfig

  • Step 4.2: Save the configuration

  • Step 4.3: Exit the menuconfig

• Step 5: Do Pre-Build checks

  • Step 5.1: Check .config file is present or not

  • Step 5.2 : Check the location of toolchain

• Step 6: Build application package

• Step 7: Do post build checks

  • Step 7.1 Check the location of the shared library file

  • Step 7.2: Check the “objdump” output of the static library file

  • Step 7.3: Check the “readelf” output of the static library file

  • Step 7.4: Check the “nm” output of the application binary file

  • Step 7.5: Check the “file” command output of static library (.a) file

  • Step 7.6: Check the “size” command output of static library file

  • Step 7.7: Check the “strings” command output of static library file

  • Step 7.8: Check the location of .ipk file

  • Step 7.9: How to extract .ipk file

  • Step 7.10: How to check content of .ipk file

• Step 8: Build full openwrt - Incremental

  • Step 8.1: Do Pre-Build checks

  • Step 8.2: Build full openwrt

  • Step 8.3: Do Post-Build checks

Topics in this section,

PART B: CREATING STATIC APPLICATION

• Step 1: Add custom application

  • Step 1.1: Add directory structure of “Static Application” package

  • Step 1.2: Create directory under package/libs directory

  • Step 1.3: Create directories under x_static_app directory

  • Step 1.4: Create app.c under src directory

  • Step 1.5: Create my_static_lib.h under inc directory

  • Step 1.6: Create Makefile in “x_static_app” directory

  • Step 1.7: Explanation of Makefile part by part

• Step 2 : Add application package to menuconfig

  • Step 2.1: Create feeds.conf file

  • Step 2.2: Content of feeds.conf

  • Step 2.3: Below example for feeds path

• Step 3 : Update and install feeds

  • Step 3.1: Commands for update and install feeds

• Step 4 : Enable application package in menuconfig

  • Step 4.1: Select your application in menuconfig

  • Step 4.2: Save the configuration

  • Step 4.3: Exit the menuconfig

• Step 5: Do Pre-Build checks

  • Step 5.1: Check .config file is present or not

  • Step 5.2 : Check the location of toolchain

• Step 6: Build application package

• Step 7: Do post build checks

  • Step 7.1 Check the location of the static application binary file

  • Step 7.2: Check the “objdump” output of the static application file

  • Step 7.3: Check the “readelf” output of the static application file

  • Step 7.4: Check the “nm” output of the static application file

  • Step 7.5: Check the “file” command output of static application file

  • Step 7.6: Check the “size” command output of static application file

  • Step 7.7: Check the “strings” command output of static application file

  • Step 7.8: Check the location of .ipk file

  • Step 7.9: How to extract .ipk file

  • Step 7.10: How to check content of .ipk file

• Step 8: Build full openwrt - Incremental

  • Step 8.1: Do Pre-Build checks

  • Step 8.2: Build full openwrt

  • Step 8.3: Do Post-Build checks

Note

PART A: Creating Static Library

Note

Create 2 folders in alphabet order so that library side makefile should execute first and it will create .a static library file

Step 1 : Add custom built library

In this section you will learn how to add custom built library in “Openwrt”

Step 1.1: Add directory structure of “Static Library” application package

• Make sure the current directory “openwrt”

  $ pwd
  
    /home/test/openwrt
  

Step 1.2: Create directory under package/libs directory

• Make sure the current directory “openwrt”

  $ cd package/libs/
  
  $ mkdir -p static_lib/my_static_lib
  

Step 1.3: Create directories under my_static_lib directory

• Make sure the current directory “my_static_lib”

  $ cd my_static_lib
  
  $ mkdir src obj inc
  

Step 1.4: Create my_static_lib.c under src directory

• Make sure the current directory “my_static_lib/src”

• In my_static_lib.c have “Function Definition”

• Create my_static_lib.c file using vim command

vim my_static_lib.c

• Content of src/my_static_lib.c

#include "my_static_lib.h"

void my_static_function(void)
{
       printf("Hello from my_static_function!\n");
}

Step 1.5: Create my_static_lib.h under inc directory

• Make sure the current directory “my_static_lib/inc”

• In my_static_lib.h have “Function Prototype”

• Create my_static_lib.h file using vim command

vim my_static_lib.h

• Content of inc/my_static_lib.h

#include <stdio.h>

void my_static_function(void);

What is Static Library ?

See Answer

• Collection of compiled object code that can be linked directly to the program at the compile time.

What are the types of library ?

See Answer

• Two types of library:

  • Static Library

  • Shared Library

What is the use of library ?

See Answer

• It is a collection of pre-compiled functions that can be used by a program.

• Used to reduce the redundancy of code

Step 1.6: Create Makefile in “my_static_lib” directory

• Make sure the current directory “my_static_lib”

• Create Makefile file using vim command

  vim Makefile
  

• Content of Makefile

  include $(TOPDIR)/rules.mk
  
  PKG_NAME:=my_static_lib
  PKG_VERSION:=1.0
  PKG_RELEASE:=1
  
  SOURCE_DIR:=$(TOPDIR)/package/libs/static_lib/my_static_lib
  
  include $(INCLUDE_DIR)/package.mk
  
  define Package/my_static_lib
  SECTION:=examples
  CATEGORY:=Examples
  TITLE:=My Static Library
  endef
  
  define Package/my_static_lib/description
          A simple static library example
  endef
  
  define Build/Prepare
          mkdir -p $(PKG_BUILD_DIR)
          cp -r $(SOURCE_DIR)/src $(PKG_BUILD_DIR)
          cp -r $(SOURCE_DIR)/inc $(PKG_BUILD_DIR)
          cp -r $(SOURCE_DIR)/obj $(PKG_BUILD_DIR)
          cp $(SOURCE_DIR)/Makefile $(PKG_BUILD_DIR)
          $(Build/Patch)
  endef
  
  define Build/Compile
          $(TARGET_CC) $(TARGET_CFLAGS) -I$(PKG_BUILD_DIR)/inc -o $(PKG_BUILD_DIR)/obj/my_static_lib.o -c $(PKG_BUILD_DIR)/src/my_static_lib.c
          $(TARGET_AR) -rc $(PKG_BUILD_DIR)/obj/libmy_static_lib.a $(PKG_BUILD_DIR)/obj/my_static_lib.o
  endef
  
  define Package/my_static_lib/install
          $(INSTALL_DIR) $(1)/usr/lib
          $(INSTALL_BIN) $(PKG_BUILD_DIR)/obj/libmy_static_lib.a $(1)/usr/lib/
  endef
  
  $(eval $(call BuildPackage,my_static_lib))
  

Step 1.7: Explanation of Makefile part by part

include $(TOPDIR)/rules.mk

• Explanation of include $(TOPDIR)/rules.mk

  include $(TOPDIR)/rules.mk
  

• The $(TOPDIR) is expected to be the top-level directory

• /rules.mk - The path to the file included

What is $(TOPDIR) ?

See Answer

• $(TOPDIR) path is /home/test/openwrt

Package Name, Version and Release number Block

• Explanation of Package Name, Version and Release number Block

PKG_NAME:=my_static_lib
PKG_VERSION:=1.0
PKG_RELEASE:=1

• The name and version of your package are used to define the variable to point to the build directory of your package (Ex: my_static_lib-1.0)

Path (absolute or relative) to a directory Block

• Explanation of SOURCE_DIR

SOURCE_DIR:=$(TOPDIR)/package/libs/static_lib/my_static_lib

What is SOURCE_DIR ?

See Answer

• SOURCE_DIR is relative or absolute path of directory

• In this case path of SOURCE_DIR $HOME/openwrt/package/libs/static_lib/my_static_lib

• Give path of the source directory

• SOURCE_DIR is used in Build/Prepare

include $(INCLUDE_DIR)/package.mk

• Explanation of include $(INCLUDE_DIR)/package.mk

include $(INCLUDE_DIR)/package.mk

• $(INCLUDE_DIR) - Directory containing include files

• /package.mk: The path to the file included

What is $(INCLUDE_DIR) ?

See Answer

• $(INCLUDE_DIR) - It will search for included files

• In this case path of $(INCLUDE_DIR) $HOME/openwrt/include

Package Information Block

• Explanation of Package Information

define Package/my_static_lib
SECTION:=examples
CATEGORY:=Examples
TITLE:=My Static Library
endef

• This block defines the package information as section, category, and title

• SECTION: examples: This line tells the section to which the package belongs. In this case, the package will come under the “examples” section.

• CATEGORY: Examples: This line tells the category to which the package belongs. In this case, the category is set to “Examples

• TITLE: My Static Library This line tells, title or name of the package. In this case, the title is set to “My Static Library”.

• endef: This line will be the end of the define block.

What all information included in Package Information Block ?

See Answer

• It includes section, category, and title

Package Description Block

• Explanation of Package Description

define Package/my_static_lib/description
        A simple static library example
endef

• This function defines of package.

What is Package Description Block ?

See Answer

• Instructs on how and where our package will appear in the overall configuration menu

Build/Prepare Block

• Explanation of Build/Prepare

define Build/Prepare
        mkdir -p $(PKG_BUILD_DIR)
        cp -r $(SOURCE_DIR)/src $(PKG_BUILD_DIR)
        cp -r $(SOURCE_DIR)/inc $(PKG_BUILD_DIR)
        cp -r $(SOURCE_DIR)/obj $(PKG_BUILD_DIR)
        cp $(SOURCE_DIR)/Makefile $(PKG_BUILD_DIR)
        $(Build/Patch)
endef

• mkdir -p $(PKG_BUILD_DIR): This line creates the build directory

• cp -r $(SOURCE_DIR)/src $(PKG_BUILD_DIR): This line copies the contents from SOURCE_DIR (source) to PKG_BUILD_DIR (destination)

• cp -r $(SOURCE_DIR)/inc $(PKG_BUILD_DIR): This line copies the contents from SOURCE_DIR (source) to PKG_BUILD_DIR (destination)

• cp -r $(SOURCE_DIR)/obj $(PKG_BUILD_DIR): This line copies the contents from SOURCE_DIR (source) to PKG_BUILD_DIR (destination)

• cp -r $(SOURCE_DIR)Makefile $(PKG_BUILD_DIR): This line copies the contents from SOURCE_DIR (source) to PKG_BUILD_DIR (destination)

• -r : -r is recursive copy.

• $(Build/Patch): This line includes a call to $(Build/Patch), which is a variable or macro typically defined elsewhere in the Makefile. It is used to apply any necessary patches to the source code.

What is -r ?

See Answer

• -r is recursive copy.

Which path $(PKG_BUILD_DIR) ?

See Answer

• In this case path of $(PKG_BUILD_DIR) $HOME/openwrt/build_dir/target-aarch64_cortex-a72_musl/my_static_lib-1.0

What is SOURCE_DIR ?

See Answer

• In this case path of SOURCE_DIR $HOME/openwrt/package/mypackages/examples/my_static_lib

Build/Compile Block

• Explanation of Build/Compile

define Build/Compile
        $(TARGET_CC) $(TARGET_CFLAGS) -I$(PKG_BUILD_DIR)/inc -o $(PKG_BUILD_DIR)/obj/my_static_lib.o -c $(PKG_BUILD_DIR)/src/my_static_lib.c
        $(TARGET_AR) -rc $(PKG_BUILD_DIR)/obj/libmy_static_lib.a $(PKG_BUILD_DIR)/obj/my_static_lib.o
endef

• This block defines the compilation process.

• $(TARGET_CC): It is said to arm cross compiler and it is defined globally

• $(TARGET_CFLAGS): It is used for additional flags

• -I$(PKG_BUILD_DIR)/inc : It will include prototype path

• -o $(PKG_BUILD_DIR)/obj/my_static_lib.o : Takes .c input file and generates .o output file in location $(PKG_BUILD_DIR)/obj

• $(TARGET_AR): It is used as archive tool.

• $(TARGET_AR): aarch64-openwrt-linux-musl-gcc-ar

• In this case path of $(TARGET_AR) $HOME/openwrt/staging_dir/toolchain-aarch64_cortex-a72_gcc-12.3.0_musl/bin/aarch64-openwrt-linux-musl-gcc-ar

• $(PKG_BUILD_DIR)/obj/libmy_static_lib.a : Takes .o input file and generates .a output file in location $(PKG_BUILD_DIR)/obj

What is $(TARGET_CC) ?

See Answer

• It is said to arm cross compiler

• In this case path of $(TARGET_CC) $HOME/openwrt/staging_dir/toolchain-aarch64_cortex-a72_gcc-12.3.0_musl

What is $(TARGET_CFLAGS) ?

See Answer

• It is used for additional flags

What is $(TARGET_AR) ?

See Answer

• $(TARGET_AR): It is used as archive tool.

• $(TARGET_AR): aarch64-openwrt-linux-musl-gcc-ar

• In this case path of $(TARGET_AR) $HOME/openwrt/staging_dir/toolchain-aarch64_cortex-a72_gcc-12.3.0_musl/bin/aarch64-openwrt-linux-musl-gcc-ar

Package Install Block

• Explanation of Package Install

define Package/my_static_lib/install
        $(INSTALL_DIR) $(1)/usr/lib
        $(INSTALL_BIN) $(PKG_BUILD_DIR)/obj/libmy_static_lib.a $(1)/usr/lib/
endef

• $(INSTALL_DIR): It used for creating a directory and it is commonly used in build systems like OpenWrt.

• $(INSTALL_BIN): It used for copying an executable file.

• In this case path of $(PKG_BUILD_DIR) $HOME/openwrt/build_dir/target-aarch64_cortex-a72_musl/my_static_lib-1.0

• /usr/bin: It is the destination directory, .a file will be installed.

What is $(INSTALL_DIR) ?

See Answer

• It used for creating a directory

• In this case $(INSTALL_DIR) install -d -m0755

• Install command is used to copy files and set attributes.

• -d, –directory : It will act as directory names towards all arguments.

• m, –mode=MODE : Set permission mode (as in chmod).

What is $(INSTALL_BIN) ?

See Answer

• It used for copying an executable file.

• In this case $(INSTALL_BIN) install -m0755

• m, –mode=MODE : Set permission mode (as in chmod).

What is $(1)/usr/bin ?

See Answer

• /usr/bin: It is the destination directory where the binary executable will be installed.

• In this case path of $(1)/usr/bin $HOME/openwrt/build_dir/target-aarch64_cortex-a72_musl/my_static_lib-1.0/.pkgdir/my_static_lib/usr/lib

Package Build Block

• Explanation of Package Build

$(eval $(call BuildPackage,my_static_lib))

• BuildPackage: It is function call with my_static_lib as parameter.

Step 2 : Add application package to menuconfig

In this section you will learn how to add menuconfig

Step 2.1: Create feeds.conf file

• Make sure the current directory is “openwrt”

• Create new feeds.conf file using vim command in openwrt directory

$ vim feeds.conf

Step 2.2: Content of feeds.conf

• Inside feeds.conf

src-link <name> <path>

Step 2.3: Below example for feeds path

• Make sure the current directory is “openwrt”

• Create new feeds.conf file using vim command in openwrt directory

src-link libs /home/test/openwrt/package/libs

Step 3 : Update and install feeds

In this section you will learn how to install and update feeds

Step 3.1: Commands for update and install feeds

• Installs the most recent packages, replacing any earlier versions that were already on your system

$ ./scripts/feeds update -a

$ ./scripts/feeds install -a -f

Step 4 : Enable application package in menuconfig

In this section you will learn how to enable in menuconfig

Step 4.1: Select your application in menuconfig

• Select your category that reflects in menuconfig

• Go inside examples and select my_static_lib

Step 4.2: Save the configuration

Step 4.3: Exit the menuconfig

Step 5: Do Pre-Build checks

In this section you will learn how to do Pre-build checks

Step 5.1: Check .config file is present or not

• In .config file package should be enabled in ‘y’

• Below line should be present in .config file

  CONFIG_PACKAGE_my_static_lib=y
  

Step 5.2 : Check the location of toolchain

• Make sure the current directory “openwrt”

  $HOME/openwrt/staging_dir/toolchain-aarch64_cortex-a72_gcc-12.3.0_musl/aarch64-openwrt-linux-musl
  

  $ ls -l
  
   drwxr-xr-x 2 sysadmin sysadmin 4096 Dec 23 02:58 bin
   drwxr-xr-x 3 sysadmin sysadmin 4096 Dec 23 03:39 include
   lrwxrwxrwx 1 sysadmin sysadmin    6 Dec 23 03:39 lib -> ../lib
   lrwxrwxrwx 1 sysadmin sysadmin    8 Dec 23 03:20 lib64 -> ../lib64
   lrwxrwxrwx 1 sysadmin sysadmin   10 Dec 23 03:39 sys-include -> ../include
  

Step 6: Build application package

• Make sure the current directory is “openwrt”

  $HOME/openwrt
  
  $ make package/my_static_lib/compile
  

Step 7: Do post build checks

In this section you will learn about post build checks

Step 7.1 Check the location of the static library file

• Make sure the current directory is ‘my_static_lib-1.0’

  $HOME/openwrt/build_dir/target-aarch64_cortex-a72_musl/my_static_lib-1.0
  
  $ ls -l
  
  drwxr-xr-x 2 sysadmin sysadmin 4096 Jan  5 21:27 inc
  drwxr-xr-x 3 sysadmin sysadmin 4096 Jan  5 21:27 ipkg-aarch64_cortex-a72
  -rw-r--r-- 1 sysadmin sysadmin 2576 Jan  5 21:27 Makefile
  drwxr-xr-x 2 sysadmin sysadmin 4096 Jan  5 21:27 obj
  drwxr-xr-x 2 sysadmin sysadmin 4096 Jan  5 21:27 src
  

$ cd src

$ ls -l

-rw-r--r-- 1 sysadmin sysadmin 139 Jan  5 21:27 my_static_lib.c

$ cd inc

$ ls -l

-rw-r--r-- 1 sysadmin sysadmin 50 Jan  5 21:27 my_static_lib.h

$ cd obj

$ ls -l

-rw-r--r-- 1 sysadmin sysadmin 1756 Jan  5 21:27 libmy_static_lib.a
-rw-r--r-- 1 sysadmin sysadmin 1600 Jan  5 21:27 my_static_lib.o

See that object file called my_static_lib.o is present inside directory ?

See Answer

$HOME/openwrt/build_dir/target-aarch64_cortex-a72_musl/my_static_lib-1.0/obj

$ ls -l

• -rw-r–r– 1 sysadmin sysadmin 1600 Jan 5 21:27 my_static_lib.o

See that .a file called libmy_static_lib.a is present inside directory ?

See Answer

$HOME/openwrt/build_dir/target-aarch64_cortex-a72_musl/my_static_lib-1.0/obj

$ ls -l

• -rw-r–r– 1 sysadmin sysadmin 1756 Jan 5 21:27 libmy_static_lib.a

Step 7.2: Check the “objdump” output of the static library file

Step 7.2.1: Check “objdump” -t

• Let check objdump” output of the static library file

• objdump -t : Displays the symbols of application binary file

• Check if “my_static_function” is present or not in the “objdump”

• Make sure the current directory “obj”

$ pwd

$HOME/openwrt/build_dir/target-aarch64_cortex-a72_musl/my_static_lib-1.0/obj

$ ls -l

-rw-r--r-- 1 sysadmin sysadmin 1756 Jan  7 10:04 libmy_static_lib.a
-rw-r--r-- 1 sysadmin sysadmin 1600 Jan  7 10:04 my_static_lib.o

$HOME/openwrt/staging_dir/toolchain-aarch64_cortex-a72_gcc-12.3.0_musl/aarch64-openwrt-linux-musl/bin/objdump libmy_static_lib.a -t | grep -i my_static_function

0000000000000000 g     F .text     000000000000000c my_static_function

Step 7.2.2: Check “objdump” -S

• objdump -S : Display source code intermixed with disassembly

• Check if “my_static_function” is present or not in the “objdump”

• Make sure the current directory “obj”

$ pwd

$HOME/openwrt/build_dir/target-aarch64_cortex-a72_musl/my_static_lib-1.0/obj

$ ls -l

-rw-r--r-- 1 sysadmin sysadmin 1756 Jan  7 10:04 libmy_static_lib.a
-rw-r--r-- 1 sysadmin sysadmin 1600 Jan  7 10:04 my_static_lib.o

$HOME/openwrt/staging_dir/toolchain-aarch64_cortex-a72_gcc-12.3.0_musl/aarch64-openwrt-linux-musl/bin/objdump libmy_static_lib.a -S | grep -i my_static_function

0000000000000000 <my_static_function>:
0:      90000000        adrp    x0, 0 <my_static_function>

What is “-S” option is used in “objdump” command ?

See Answer

• -S : Display source code intermixed with disassembly

What “objdump” command does ?

See Answer

• The “objdump” tool is to debug and understand the executable file

• Symbols “my_static_function” are present in .a static library file

• Hence we can confirm application is compiled successfully

Step 7.3: Check the “readelf” output of the static library file

Step 7.3.1: Check “readelf” -s

• readelf -s: Display the symbol table

• Check if “my_static_function” is present or not in the “readelf”

• Make sure the current directory “obj”

$ pwd

$HOME/openwrt/build_dir/target-aarch64_cortex-a72_musl/my_static_lib-1.0/obj

$ ls -l

-rw-r--r-- 1 sysadmin sysadmin 1756 Jan  7 10:04 libmy_static_lib.a
-rw-r--r-- 1 sysadmin sysadmin 1600 Jan  7 10:04 my_static_lib.o

$HOME/openwrt/staging_dir/toolchain-aarch64_cortex-a72_gcc-12.3.0_musl/aarch64-openwrt-linux-musl/bin/readelf libmy_static_lib.a -s | grep -i my_static_function

11: 0000000000000000    12 FUNC    GLOBAL DEFAULT    1 my_static_function

What is “-s” option is used in “readelf” command ?

See Answer

• -s: Display the symbol table

What “readelf” command does ?

See Answer

• readelf: Display information about ELF files

What is the purpose of “readelf” command ?

See Answer

• The main purpose of the readelf tool is to display the headers of an ELF (Executable and Linkable Format) files

• Symbols “my_static_function” are present in .a static library file

• Hence we can confirm application is compiled successfully

Step 7.4: Check the “nm” output of the static library file

Step 7.4.1: Check “nm” -S

• nm -S: Print both value and size of defined symbols for the “bsd” output style

• Check if “my_static_function” is present or not in the “nm”

• Make sure the current directory “obj”

$ pwd

$HOME/openwrt/build_dir/target-aarch64_cortex-a72_musl/my_static_lib-1.0/obj

$ ls -l

-rw-r--r-- 1 sysadmin sysadmin 1756 Jan  7 10:04 libmy_static_lib.a
-rw-r--r-- 1 sysadmin sysadmin 1600 Jan  7 10:04 my_static_lib.o

$HOME/openwrt/staging_dir/toolchain-aarch64_cortex-a72_gcc-12.3.0_musl/aarch64-openwrt-linux-musl/bin/nm libmy_static_lib.a -S | grep -i my_static_function

0000000000000000 000000000000000c T my_static_function

What is “-S” option is used in “nm” command ?

See Answer

• -S: Print both value and size of defined symbols for the “bsd” output style

What “nm” command does ?

See Answer

• nm is used to dump the symbol table and their attributes from a binary executable file.

What is the purpose of “nm” command ?

See Answer

• The main purpose of the nm tool is to display information about symbols in the specified File, which can be an object file, an executable file, or an object-file library.

• Symbols “my_static_function” are present in .a static library file

• Hence we can confirm application is compiled successfully

Step 7.4.2: Check “nm” -s

• nm -s: When listing symbols from archive members, include the index: a mapping of which modules contain definitions for which names.

• Check if “my_static_function” is present or not in the “nm”

• Make sure the current directory “obj”

$ pwd

$HOME/openwrt/build_dir/target-aarch64_cortex-a72_musl/my_static_lib-1.0/obj

$ ls -l

-rw-r--r-- 1 sysadmin sysadmin 1756 Jan  7 10:04 libmy_static_lib.a
-rw-r--r-- 1 sysadmin sysadmin 1600 Jan  7 10:04 my_static_lib.o

$HOME/openwrt/staging_dir/toolchain-aarch64_cortex-a72_gcc-12.3.0_musl/aarch64-openwrt-linux-musl/bin/nm libmy_static_lib.a -s | grep -i my_static_function

my_static_function in my_static_lib.o
0000000000000000 T my_static_function

• Symbols “my_static_function” are present in .a static library file

• Hence we can confirm application is compiled successfully

Step 7.5: Check the “file” command output of static library (.a) file

• file: Determine file type

$ file libmy_static_lib.a

libmy_static_lib.a: current ar archive

Why “file” command is used ?

See Answer

• file command is used to determine the file type.

Step 7.5.1: Check the “file” command output of static library object file

$ file my_static_lib.o

my_static_lib.o: ELF 64-bit LSB relocatable, ARM aarch64, version 1 (SYSV), not stripped

Step 7.6: Check the “size” command output of static library file

• size: List section sizes and total size of binary files

$ size libmy_static_lib.a

  text    data     bss     dec     hex filename
  85         0       0      85      55 my_static_lib.o (ex libmy_static_lib.a)

What “size” command does ?

See Answer

• size command will display the output that will give you information on the size command in 5 values like data, text, dec, bss, and hex

Step 7.7: Check the “strings” command output of static library file

• strings - print the sequences of printable characters in files

• As we can see string output are added in the program are confirmed.

$ strings libmy_static_lib.a | grep -i Hello

  Hello from my_static_function!

What “strings” command does ?

See Answer

• strings command is used to return the string characters into files.

Step 7.8: Check the location of .ipk file

• Make sure the current directory “openwrt”

$HOME/openwrt/staging_dir/packages/bcm27xx

$ ls -l | grep -i "my_static_lib"

 lrwxrwxrwx 1 sysadmin sysadmin 123 Jan  5 19:30 my_static_lib_1.0-1_aarch64_cortex-a72.ipk -> /home/test/openwrt/bin/packages/aarch64_cortex-a72/libs/my_static_lib_1.0-1_aarch64_cortex-a72.ipk

• ipk file: It is compressed archive format derived from the Debian package (. DEB) format

What is “IPK” file ?

See Answer

• IPK file is a compressed archive format derived from the Debian package (. DEB) format

Step 7.9: How to extract .ipk file

• Make sure the current directory “openwrt”

$HOME/openwrt/staging_dir/packages/bcm27xx

• Command to extract .ipk file is below

$ tar -xzf my_static_lib_1.0-1_aarch64_cortex-a72.ipk

$ ls

  control.tar.gz
  data.tar.gz
  debian-binary

what is the command to extract IPK file ?

See Answer

• tar -xzf my_static_lib_1.0-1_aarch64_cortex-a72.ipk

Step 7.10: How to check content of .ipk file

• First extract control.tar.gz and data.tar.gz

• Command to check content for control.tar.gz file is below

$ tar -xzvf control.tar.gz

./control
./postinst
./prerm

• Check ./control using “vim command”

$ vim ./control

• Content of ./control

Package: my_static_lib
Version: 1.0-1
Depends: libc
Source: package/libs/static_lib/my_static_lib
SourceName: my_static_lib
Section: examples
SourceDateEpoch: 1703276774
Architecture: aarch64_cortex-a72
Installed-Size: 684
Description:  A simple static library example

• Check inside for other files ./postinst and ./prerm using “vim” command

• Command to check content for control.tar.gz file is below

$ tar -xzvf data.tar.gz

 ./usr/
 ./usr/lib/
 ./usr/lib/libmy_static_lib.a

• Check ./usr/lib/libmy_static_lib.a is a static library file

Step 8: Build full openwrt - Incremental

In this section you will learn how to build full openwrt

Step 8.1: Do Pre-Build checks

• Make sure the current directory “openwrt”

$HOME/openwrt

Step 8.2: Build full openwrt

$ make -j1 V=s

• It compile all packages

• -j1: This option tells the build system work on one task at a time.

• V=s: This sets the verbosity level to ‘s’, which means “silent” or “verbose.” When set to ‘s’, it makes the build system display more detailed information about what it’s doing. You’ll see the commands it’s running and the files it’s working on. This verbose output is helpful for understanding and debugging the build process.

Step 8.3: Do Post-Build checks

Step 8.3.1 : Check the location of the full image

• Make sure the current directory “openwrt”

• To check package is successfully compiled, below is the path

$HOME/openwrt/bin/targets/bcm27xx/bcm2711

• To check the image file is present or not

$ ls -l

-rw-r--r-- 1 sysadmin sysadmin      1655 Jan  5 19:29 config.buildinfo
-rw-r--r-- 1 sysadmin sysadmin        71 Jan  5 19:29 feeds.buildinfo
-rw-r--r-- 1 sysadmin sysadmin 184549376 Jan  5 16:04 openwrt-bcm27xx-bcm2711-rpi-4-ext4-factory.img
-rw-r--r-- 1 sysadmin sysadmin  17114759 Jan  5 19:30 openwrt-bcm27xx-bcm2711-rpi-4-ext4-factory.img.gz
-rw-r--r-- 1 sysadmin sysadmin  17115606 Jan  5 19:30 openwrt-bcm27xx-bcm2711-rpi-4-ext4-sysupgrade.img.gz
-rw-r--r-- 1 sysadmin sysadmin      4210 Jan  5 19:30 openwrt-bcm27xx-bcm2711-rpi-4.manifest
-rw-r--r-- 1 sysadmin sysadmin  15351510 Jan  5 19:30 openwrt-bcm27xx-bcm2711-rpi-4-squashfs-factory.img.gz
-rw-r--r-- 1 sysadmin sysadmin  15352357 Jan  5 19:30 openwrt-bcm27xx-bcm2711-rpi-4-squashfs-sysupgrade.img.gz
drwxr-xr-x 2 sysadmin sysadmin      4096 Jan  5 19:30 packages
-rw-r--r-- 1 sysadmin sysadmin      2141 Jan  5 19:30 profiles.json
-rw-r--r-- 1 sysadmin sysadmin      1025 Jan  5 19:31 sha256sums
-rw-r--r-- 1 sysadmin sysadmin        18 Jan  5 19:29 version.buildinfo

• As we can see “image” is present then it is confirmed that fully image is successfull

• Image file is openwrt-bcm27xx-bcm2711-rpi-4-ext4-factory.img.gz

Step 8.3.2 : How to extract full image file

• To extract image file command and pathis below

• Make sure the current directory “openwrt”

$HOME/openwrt/bin/targets/bcm27xx/bcm2711

$ ls -l

-rw-r--r-- 1 sysadmin sysadmin      1655 Jan  5 19:29 config.buildinfo
-rw-r--r-- 1 sysadmin sysadmin        71 Jan  5 19:29 feeds.buildinfo
-rw-r--r-- 1 sysadmin sysadmin  17114759 Jan  5 19:30 openwrt-bcm27xx-bcm2711-rpi-4-ext4-factory.img.gz
-rw-r--r-- 1 sysadmin sysadmin  17115606 Jan  5 19:30 openwrt-bcm27xx-bcm2711-rpi-4-ext4-sysupgrade.img.gz
-rw-r--r-- 1 sysadmin sysadmin      4210 Jan  5 19:30 openwrt-bcm27xx-bcm2711-rpi-4.manifest
-rw-r--r-- 1 sysadmin sysadmin  15351510 Jan  5 19:30 openwrt-bcm27xx-bcm2711-rpi-4-squashfs-factory.img.gz
-rw-r--r-- 1 sysadmin sysadmin  15352357 Jan  5 19:30 openwrt-bcm27xx-bcm2711-rpi-4-squashfs-sysupgrade.img.gz
drwxr-xr-x 2 sysadmin sysadmin      4096 Jan  5 19:30 packages
-rw-r--r-- 1 sysadmin sysadmin      2141 Jan  5 19:30 profiles.json
-rw-r--r-- 1 sysadmin sysadmin      1025 Jan  5 19:31 sha256sums
-rw-r--r-- 1 sysadmin sysadmin        18 Jan  5 19:29 version.buildinfo

• Command to extract full image file

$ gunzip -d openwrt-bcm27xx-bcm2711-rpi-4-ext4-factory.img.gz

• After extracting image file check with ls command it will display below file

$ ls -l

 -rw-r--r-- 1 sysadmin sysadmin 184549376 Jan  5 19:30 openwrt-bcm27xx-bcm2711-rpi-4-ext4-factory.img

Step 8.3.3: Check the content of image file

• Content of full image file

Step 8.3.4 : Check the size of the full image

• The du (disk usage) that allows users to analyze and report on disk usage within directories and files.

• Displays sizes in human-readable format, using units such as KB, MB, GB, etc.

$ du -h openwrt-bcm27xx-bcm2711-rpi-4-ext4-factory.img.gz

17M     openwrt-bcm27xx-bcm2711-rpi-4-ext4-factory.img.gz

• As we can see size of image file is around 17M

Note

PART B: Creating Static Application

Step 1 : Add custom built library

In this section you will learn how to add custom built library in “Openwrt”

Step 1.1: Add directory structure of “Static Application” package

• Make sure the current directory “openwrt”

  $ pwd
  
    /home/test/openwrt
  

Step 1.2: Create directory under package/libs directory

• Make sure the current directory “openwrt”

  $ cd package/libs/static_lib
  
  $ mkdir x_static_app
  

Step 1.3: Create directories under x_static_app directory

• Make sure the current directory “x_static_app”

  $ cd x_static_app
  
  $ mkdir src obj inc
  

Step 1.4: Create app.c under src directory

• Make sure the current directory “x_static_app/src”

• In app.c have “Function calling”

• Create app.c file using vim command

vim app.c

• Content of src/app.c

#include <stdio.h>
#include "my_static_lib.h"

extern void my_static_function(void);

int main(void)
{
       my_static_function();

       return 0;
}

Step 1.5: Create my_static_lib.h under inc directory

• Make sure the current directory “x_static_app/inc”

• In my_static_lib.h have “Function Prototype”

• Create my_static_lib.h file using vim command

vim my_static_lib.h

• Content of inc/my_static_lib.h

#include <stdio.h>

void my_static_function(void);

Step 1.6: Create Makefile in “x_static_app” directory

• Make sure the current directory “x_static_app”

• Create Makefile file using vim command

  vim Makefile
  

• Content of Makefile

  include $(TOPDIR)/rules.mk
  
  PKG_NAME:=x_static_app
  PKG_VERSION:=1.0
  PKG_RELEASE:=1
  
  SOURCE_DIR:=$(TOPDIR)/package/libs/static_lib/x_static_app
  
  include $(INCLUDE_DIR)/package.mk
  
  define Package/x_static_app
          SECTION:=examples
          CATEGORY:=Examples
          TITLE:=My Static Library
          DEPENDS:=+my_static_lib
  endef
  
  define Package/x_static_app/description
          A simple static library example
  endef
  
  define Build/Prepare
          mkdir -p $(PKG_BUILD_DIR)
          cp -r $(SOURCE_DIR)/src $(PKG_BUILD_DIR)
          cp -r $(SOURCE_DIR)/inc $(PKG_BUILD_DIR)
          cp -r $(SOURCE_DIR)/obj $(PKG_BUILD_DIR)
          cp $(SOURCE_DIR)/Makefile $(PKG_BUILD_DIR)
          $(Build/Patch)
  endef
  
  define Build/Compile
          $(TARGET_CC) -I$(PKG_BUILD_DIR)/inc $(PKG_BUILD_DIR)/src/app.c -L/home/test/openwrt/build_dir/target-aarch64_cortex-a72_musl/my_static_lib-1.0/obj -l my_static_lib -o $(PKG_BUILD_DIR)/obj/app
  endef
  
  define Package/x_static_app/install
          $(INSTALL_DIR) $(1)/usr/bin
          $(INSTALL_BIN) $(PKG_BUILD_DIR)/obj/app $(1)/usr/bin/
  endef
  
  $(eval $(call BuildPackage,x_static_app))
  

Step 1.7: Explanation of Makefile part by part

include $(TOPDIR)/rules.mk

• Explanation of include $(TOPDIR)/rules.mk

  include $(TOPDIR)/rules.mk
  

• The $(TOPDIR) is expected to be the top-level directory

• /rules.mk - The path to the file included

What is $(TOPDIR) ?

See Answer

• $(TOPDIR) path is /home/test/openwrt

Package Name, Version and Release number Block

• Explanation of Package Name, Version and Release number Block

PKG_NAME:=x_static_app
PKG_VERSION:=1.0
PKG_RELEASE:=1

• The name and version of your package are used to define the variable to point to the build directory of your package (Ex: a_static_app-1.0)

Path (absolute or relative) to a directory Block

• Explanation of SOURCE_DIR

SOURCE_DIR:=$(TOPDIR)/package/libs/static_lib/x_static_app

What is SOURCE_DIR ?

See Answer

• SOURCE_DIR is relative or absolute path of directory

• In this case path of SOURCE_DIR $HOME/openwrt/package/libs/static_lib/x_static_app

• Give path of the source directory

• SOURCE_DIR is used in Build/Prepare

include $(INCLUDE_DIR)/package.mk

• Explanation of include $(INCLUDE_DIR)/package.mk

include $(INCLUDE_DIR)/package.mk

• $(INCLUDE_DIR) - Directory containing include files

• /package.mk: The path to the file included

What is $(INCLUDE_DIR) ?

See Answer

• $(INCLUDE_DIR) - It will search for included files

• In this case path of $(INCLUDE_DIR) $HOME/openwrt/include

Package Information Block

• Explanation of Package Information

define Package/x_static_app
   SECTION:=examples
   CATEGORY:=Examples
   TITLE:=My Static Library
   DEPENDS:=+my_static_lib
endef

• This block defines the package information as section, category, and title

• SECTION: examples: This line tells the section to which the package belongs. In this case, the package will come under the “examples” section.

• CATEGORY: Examples: This line tells the category to which the package belongs. In this case, the category is set to “Examples

• TITLE: My Static Library This line tells, title or name of the package. In this case, the title is set to “My Static Library”.

• DEPENDS: =+my_static_lib: It is the library dependencies of the package.

• endef: This line will be the end of the define block.

What all information included in Package Information Block ?

See Answer

• It includes section, category, and title

Package Description Block

• Explanation of Package Description

define Package/x_static_app/description
        A simple static library example
endef

• This function defines of package.

What is Package Description Block ?

See Answer

• Instructs on how and where our package will appear in the overall configuration menu

Build/Prepare Block

• Explanation of Build/Prepare

define Build/Prepare
        mkdir -p $(PKG_BUILD_DIR)
        cp -r $(SOURCE_DIR)/src $(PKG_BUILD_DIR)
        cp -r $(SOURCE_DIR)/inc $(PKG_BUILD_DIR)
        cp -r $(SOURCE_DIR)/obj $(PKG_BUILD_DIR)
        cp $(SOURCE_DIR)/Makefile $(PKG_BUILD_DIR)
        $(Build/Patch)
endef

• mkdir -p $(PKG_BUILD_DIR): This line creates the build directory

• cp -r $(SOURCE_DIR)/src $(PKG_BUILD_DIR): This line copies the contents from SOURCE_DIR (source) to PKG_BUILD_DIR (destination)

• cp -r $(SOURCE_DIR)/inc $(PKG_BUILD_DIR): This line copies the contents from SOURCE_DIR (source) to PKG_BUILD_DIR (destination)

• cp -r $(SOURCE_DIR)/obj $(PKG_BUILD_DIR): This line copies the contents from SOURCE_DIR (source) to PKG_BUILD_DIR (destination)

• cp -r $(SOURCE_DIR)Makefile $(PKG_BUILD_DIR): This line copies the contents from SOURCE_DIR (source) to PKG_BUILD_DIR (destination)

• -r : -r is recursive copy.

• $(Build/Patch): This line includes a call to $(Build/Patch), which is a variable or macro typically defined elsewhere in the Makefile. It is used to apply any necessary patches to the source code.

What is -r ?

See Answer

• -r is recursive copy.

Which path $(PKG_BUILD_DIR) ?

See Answer

• In this case path of $(PKG_BUILD_DIR) $HOME/openwrt/build_dir/target-aarch64_cortex-a72_musl/x_static_app-1.0

What is SOURCE_DIR ?

See Answer

• In this case path of SOURCE_DIR $HOME/openwrt/package/mypackages/examples/x_static_app

Build/Compile Block

• Explanation of Build/Compile

define Build/Compile
        $(TARGET_CC) -I$(PKG_BUILD_DIR)/inc $(PKG_BUILD_DIR)/src/app.c -L/home/test/openwrt/build_dir/target-aarch64_cortex-a72_musl/my_static_lib-1.0/obj -l my_static_lib -o $(PKG_BUILD_DIR)/obj/app
endef

• This block defines the compilation process.

• $(TARGET_CC): It is said to arm cross compiler and it is defined globally

• -I$(PKG_BUILD_DIR)/inc : It will include prototype path

• $(PKG_BUILD_DIR)/src/app.c : .c file path

• -L/home/test/openwrt/build_dir/target-aarch64_cortex-a72_musl/my_static_lib-1.0/obj : Giving the path of .a file which already generated at “Static Library” side

• l my_static_lib : It will link during the compilation process (should give 1 space after –l)

• How to give path for -L

• It is most important to check before giving path in “Static Application”

• Before copying path to –L first we need to check objdump xxxxx.a (in this case libmy_static_lib.a) with –t or –dSs it will reflect with the symbol table if not symbol table reflect then this path should not be used in –L.

• Check table of static library file

• Make sure the current directory “openwrt”

  $HOME/openwrt/build_dir/target-aarch64_cortex-a72_musl/my_static_lib-1.0/obj
  
  $ ls -l
  
  -rw-r--r-- 1 sysadmin sysadmin 1756 Jan  5 21:27 libmy_static_lib.a
  -rw-r--r-- 1 sysadmin sysadmin 1600 Jan  5 21:27 my_static_lib.o
  

• Check static library for table

  $HOME/openwrt/staging_dir/toolchain-aarch64_cortex-a72_gcc-12.3.0_musl/aarch64-openwrt-linux-musl/bin/objdump libmy_static_lib.a -dSs | grep -i my_static_function
  
  0000000000000000 <my_static_function>:
  0:      90000000        adrp    x0, 0 <my_static_function>
  

• We got the table so should give this path(.a file) to -L path in “Static Application”

What is -L ?

See Answer

• -L : It check in directory for library files

What is -l ?

See Answer

• -l : It will link with the library files

Package Install Block

• Explanation of Package Install

define Package/x_static_app/install
        $(INSTALL_DIR) $(1)/usr/bin
        $(INSTALL_BIN) $(PKG_BUILD_DIR)/obj/app $(1)/usr/bin/
endef

• $(INSTALL_DIR): It used for creating a directory and it is commonly used in build systems like OpenWrt.

• $(INSTALL_BIN): It used for copying an executable file.

• In this case path of $(PKG_BUILD_DIR) $HOME/openwrt/build_dir/target-aarch64_cortex-a72_musl/x_static_app-1.0

• /usr/bin: It is the destination directory, binary file will be installed.

What is $(INSTALL_DIR) ?

See Answer

• It used for creating a directory

• In this case $(INSTALL_DIR) install -d -m0755

• Install command is used to copy files and set attributes.

• -d, –directory : It will act as directory names towards all arguments.

• m, –mode=MODE : Set permission mode (as in chmod).

What is $(INSTALL_BIN) ?

See Answer

• It used for copying an executable file.

• In this case $(INSTALL_BIN) install -m0755

• m, –mode=MODE : Set permission mode (as in chmod).

What is $(1)/usr/bin ?

See Answer

• /usr/bin: It is the destination directory where the binary executable will be installed.

• In this case path of $(1)/usr/bin $HOME/openwrt/build_dir/target-aarch64_cortex-a72_musl/x_static_app-1.0/.pkgdir/x_static_app/usr/bin

Package Build Block

• Explanation of Package Build

$(eval $(call BuildPackage,x_static_app))

• BuildPackage: It is function call with x_static_app as parameter.

Step 2 : Add application package to menuconfig

In this section you will learn how to add menuconfig

Step 2.1: Create feeds.conf file

• Make sure the current directory is “openwrt”

• Create new feeds.conf file using vim command in openwrt directory

$ vim feeds.conf

Step 2.2: Content of feeds.conf

• Inside feeds.conf

src-link <name> <path>

Step 2.3: Below example for feeds path

• Make sure the current directory is “openwrt”

• Create new feeds.conf file using vim command in openwrt directory

src-link libs /home/test/openwrt/package/libs

Step 3 : Update and install feeds

In this section you will learn how to install and update feeds

Step 3.1: Commands for update and install feeds

• Installs the most recent packages, replacing any earlier versions that were already on your system

$ ./scripts/feeds update -a

$ ./scripts/feeds install -a -f

Step 4 : Enable application package in menuconfig

In this section you will learn how to enable in menuconfig

Step 4.1: Select your application in menuconfig

• Select your category that reflects in menuconfig

• Go inside examples and select x_static_app

Step 4.2: Save the configuration

Step 4.3: Exit the menuconfig

Step 5: Do Pre-Build checks

In this section you will learn how to do Pre-build checks

Step 5.1: Check .config file is present or not

• In .config file package should be enabled in ‘y’

• Below line should be present in .config file

  CONFIG_PACKAGE_x_static_app=y
  

Step 5.2 : Check the location of toolchain

• Make sure the current directory “openwrt”

  $HOME/openwrt/staging_dir/toolchain-aarch64_cortex-a72_gcc-12.3.0_musl/aarch64-openwrt-linux-musl
  

  $ ls -l
  
   drwxr-xr-x 2 sysadmin sysadmin 4096 Dec 23 02:58 bin
   drwxr-xr-x 3 sysadmin sysadmin 4096 Dec 23 03:39 include
   lrwxrwxrwx 1 sysadmin sysadmin    6 Dec 23 03:39 lib -> ../lib
   lrwxrwxrwx 1 sysadmin sysadmin    8 Dec 23 03:20 lib64 -> ../lib64
   lrwxrwxrwx 1 sysadmin sysadmin   10 Dec 23 03:39 sys-include -> ../include
  

Step 6: Build application package

• Make sure the current directory is “openwrt”

  $HOME/openwrt
  
  $ make package/x_static_app/compile
  

Step 7: Do post build checks

In this section you will learn about post build checks

Step 7.1 Check the location of the static application binary file

• Make sure the current directory is ‘x_static_app-1.0’

  $HOME/openwrt/build_dir/target-aarch64_cortex-a72_musl/x_static_app-1.0
  
  $ ls -l
  
  drwxr-xr-x 2 sysadmin sysadmin 4096 Jan  6 01:09 inc
  drwxr-xr-x 3 sysadmin sysadmin 4096 Jan  6 01:09 ipkg-aarch64_cortex-a72
  -rw-r--r-- 1 sysadmin sysadmin 1700 Jan  6 01:09 Makefile
  drwxr-xr-x 2 sysadmin sysadmin 4096 Jan  6 01:09 obj
  drwxr-xr-x 2 sysadmin sysadmin 4096 Jan  6 01:09 src
  

$ cd src

$ ls -l

-rw-r--r-- 1 sysadmin sysadmin 140 Jan  6 01:09 app.c

$ cd inc

$ ls -l

-rw-r--r-- 1 sysadmin sysadmin 50 Jan  6 01:09 my_static_lib.h

$ cd obj

$ ls -l

-rwxr-xr-x 1 sysadmin sysadmin 73080 Jan  6 01:09 app

Step 7.2: Check the “objdump” output of the static application file

Step 7.2.1: Check “objdump” -t

• Let check objdump” output of the static application file

• objdump -t : Displays the symbols of application binary file

• Check if “my_static_function” is present or not in the “objdump”

• Make sure the current directory “obj”

$ pwd

$HOME/openwrt/build_dir/target-aarch64_cortex-a72_musl/x_static_app-1.0/obj

$ ls -l

-rwxr-xr-x 1 sysadmin sysadmin 73080 Jan  7 10:04 app

$HOME/openwrt/staging_dir/toolchain-aarch64_cortex-a72_gcc-12.3.0_musl/aarch64-openwrt-linux-musl/bin/objdump app -t | grep -i my_static_function

00000000004005b4 g     F .text     000000000000000c              my_static_function

Step 7.2.2: Check “objdump” -S

• objdump -S : Display source code intermixed with disassembly

• Check if “my_static_function” is present or not in the “objdump”

• Make sure the current directory “obj”

$ pwd

$HOME/openwrt/build_dir/target-aarch64_cortex-a72_musl/x_static_app-1.0/obj

$ ls -l

-rwxr-xr-x 1 sysadmin sysadmin 73080 Jan  7 10:04 app

$HOME/openwrt/staging_dir/toolchain-aarch64_cortex-a72_gcc-12.3.0_musl/aarch64-openwrt-linux-musl/bin/objdump app -S | grep -i my_static_function

4005a4: 94000004        bl      4005b4 <my_static_function>
00000000004005b4 <my_static_function>:

What is “-S” option is used in “objdump” command ?

See Answer

• -S : Display source code intermixed with disassembly

What “objdump” command does ?

See Answer

• The “objdump” tool is to debug and understand the executable file

• Symbols “my_static_function” are present in app binary file

• Hence we can confirm application is compiled successfully

Step 7.3: Check the “readelf” output of the static application file

Step 7.3.1: Check “readelf” -s

• readelf -s: Display the symbol table

• Check if “my_static_function” is present or not in the “readelf”

• Make sure the current directory “obj”

$ pwd

$HOME/openwrt/build_dir/target-aarch64_cortex-a72_musl/x_static_app-1.0/obj

$ ls -l

-rwxr-xr-x 1 sysadmin sysadmin 73080 Jan  7 10:04 app

$HOME/openwrt/staging_dir/toolchain-aarch64_cortex-a72_gcc-12.3.0_musl/aarch64-openwrt-linux-musl/bin/readelf app -s | grep -i my_static_function

76: 00000000004005b4    12 FUNC    GLOBAL DEFAULT   12 my_static_function

What is “-s” option is used in “readelf” command ?

See Answer

• -s: Display the symbol table

What “readelf” command does ?

See Answer

• readelf: Display information about ELF files

What is the purpose of “readelf” command ?

See Answer

• The main purpose of the readelf tool is to display the headers of an ELF (Executable and Linkable Format) files

• Symbols “my_static_function” are present in app binary file

• Hence we can confirm application is compiled successfully

Step 7.4: Check the “nm” output of the static application file

Step 7.4.1: Check “nm” -S

• nm -S: Print both value and size of defined symbols for the “bsd” output style

• Check if “my_static_function” is present or not in the “nm”

• Make sure the current directory “obj”

$ pwd

$HOME/openwrt/build_dir/target-aarch64_cortex-a72_musl/x_static_app-1.0/obj

$ ls -l

-rwxr-xr-x 1 sysadmin sysadmin 73080 Jan  7 10:04 app

$HOME/openwrt/staging_dir/toolchain-aarch64_cortex-a72_gcc-12.3.0_musl/aarch64-openwrt-linux-musl/bin/nm app -S | grep -i my_static_function

00000000004005b4 000000000000000c T my_static_function

What is “-S” option is used in “nm” command ?

See Answer

• -S: Print both value and size of defined symbols for the “bsd” output style

What “nm” command does ?

See Answer

• nm is used to dump the symbol table and their attributes from a binary executable file.

What is the purpose of “nm” command ?

See Answer

• The main purpose of the nm tool is to display information about symbols in the specified File, which can be an object file, an executable file, or an object-file library.

• Symbols “my_static_function” are present in binary file

• Hence we can confirm application is compiled successfully

Step 7.4.2: Check “nm” -s

• nm -s: When listing symbols from archive members, include the index: a mapping of which modules contain definitions for which names.

• Check if “my_static_function” is present or not in the “nm”

• Make sure the current directory “obj”

$ pwd

$HOME/openwrt/build_dir/target-aarch64_cortex-a72_musl/x_static_app-1.0/obj

$ ls -l

-rwxr-xr-x 1 sysadmin sysadmin 73080 Jan  7 10:04 app

$HOME/openwrt/staging_dir/toolchain-aarch64_cortex-a72_gcc-12.3.0_musl/aarch64-openwrt-linux-musl/bin/nm app -s | grep -i my_static_function

00000000004005b4 T my_static_function

• Symbols “my_static_function” are present in binary application file

• Hence we can confirm application is compiled successfully

Step 7.5: Check the “file” command output of static application file

• file: Determine file type

$ file app

app: ELF 64-bit LSB executable, ARM aarch64, version 1 (SYSV), dynamically linked, interpreter /lib/ld-musl-aarch64.so.1, with debug_info, not stripped

Why “file” command is used ?

See Answer

• file command is used to determine the file type.

Step 7.6: Check the “size” command output of static application file

• size: List section sizes and total size of binary files

$ size app

  text    data     bss     dec     hex filename
  1183     616      56    1855     73f app

What “size” command does ?

See Answer

• size command will display the output that will give you information on the size command in 5 values like data, text, dec, bss, and hex

Step 7.7: Check the “strings” command output of static application file

• strings - print the sequences of printable characters in files

• As we can see string output are added in the program are confirmed.

$ strings app | grep -i my_static_function

  Hello from my_static_function!
  my_static_function

What “strings” command does ?

See Answer

• strings command is used to return the string characters into files.

Step 7.8: Check the location of .ipk file

• Make sure the current directory “openwrt”

$HOME/openwrt/staging_dir/packages/bcm27xx

$ ls -l | grep -i "x_static_app"

 lrwxrwxrwx 1 sysadmin sysadmin 122 Jan  6 01:05 x_static_app_1.0-1_aarch64_cortex-a72.ipk -> /home/test/openwrt/bin/packages/aarch64_cortex-a72/libs/x_static_app_1.0-1_aarch64_cortex-a72.ipk

• ipk file: It is compressed archive format derived from the Debian package (. DEB) format

What is “IPK” file ?

See Answer

• IPK file is a compressed archive format derived from the Debian package (. DEB) format

Step 7.9: How to extract .ipk file

• Make sure the current directory “openwrt”

$HOME/openwrt/staging_dir/packages/bcm27xx

• Command to extract .ipk file is below

$ tar -xzf x_static_app_1.0-1_aarch64_cortex-a72.ipk

$ ls

  control.tar.gz
  data.tar.gz
  debian-binary

what is the command to extract IPK file ?

See Answer

• tar -xzf x_static_app_1.0-1_aarch64_cortex-a72.ipk

Step 7.10: How to check content of .ipk file

• First extract control.tar.gz and data.tar.gz

• Command to check content for control.tar.gz file is below

$ tar -xzvf control.tar.gz

./control
./postinst
./prerm

• Check ./control using “vim command”

$ vim ./control

• Content of ./control

Package: x_static_app
Version: 1.0-1
Depends: libc, my_static_lib
Source: package/libs/static_lib/x_static_app
SourceName: x_static_app
Section: examples
SourceDateEpoch: 1703276774
Architecture: aarch64_cortex-a72
Installed-Size: 1219
Description:  A simple static library example.

• Check inside for other files ./postinst and ./prerm using “vim” command

• Command to check content for control.tar.gz file is below

$ tar -xzvf data.tar.gz

 ./usr/
 ./usr/bin/
 ./usr/bin/app

• Check ./usr/bin/app is a static application binary file

Step 8: Build full openwrt - Incremental

In this section you will learn how to build full openwrt

Step 8.1: Do Pre-Build checks

• Make sure the current directory “openwrt”

$HOME/openwrt

Step 8.2: Build full openwrt

$ make -j1 V=s

• It compile all packages

• -j1: This option tells the build system work on one task at a time.

• V=s: This sets the verbosity level to ‘s’, which means “silent” or “verbose.” When set to ‘s’, it makes the build system display more detailed information about what it’s doing. You’ll see the commands it’s running and the files it’s working on. This verbose output is helpful for understanding and debugging the build process.

Step 8.3: Do Post-Build checks

Step 8.3.1 : Check the location of the full image

• Make sure the current directory “openwrt”

• To check package is successfully compiled, below is the path

$HOME/openwrt/bin/targets/bcm27xx/bcm2711

• To check the image file is present or not

$ ls -l

-rw-r--r-- 1 sysadmin sysadmin     1685 Jan  6 01:04 config.buildinfo
-rw-r--r-- 1 sysadmin sysadmin       71 Jan  6 01:04 feeds.buildinfo
-rw-r--r-- 1 sysadmin sysadmin 17118352 Jan  6 01:05 openwrt-bcm27xx-bcm2711-rpi-4-ext4-factory.img.gz
-rw-r--r-- 1 sysadmin sysadmin 17119199 Jan  6 01:05 openwrt-bcm27xx-bcm2711-rpi-4-ext4-sysupgrade.img.gz
-rw-r--r-- 1 sysadmin sysadmin     4231 Jan  6 01:05 openwrt-bcm27xx-bcm2711-rpi-4.manifest
-rw-r--r-- 1 sysadmin sysadmin 15352083 Jan  6 01:05 openwrt-bcm27xx-bcm2711-rpi-4-squashfs-factory.img.gz
-rw-r--r-- 1 sysadmin sysadmin 15352930 Jan  6 01:05 openwrt-bcm27xx-bcm2711-rpi-4-squashfs-sysupgrade.img.gz
drwxr-xr-x 2 sysadmin sysadmin     4096 Jan  6 01:05 packages
-rw-r--r-- 1 sysadmin sysadmin     2141 Jan  6 01:06 profiles.json
-rw-r--r-- 1 sysadmin sysadmin      912 Jan  6 01:06 sha256sums
-rw-r--r-- 1 sysadmin sysadmin       18 Jan  6 01:04 version.buildinfo

• As we can see “image” is present then it is confirmed that fully image is successfull

• Image file is openwrt-bcm27xx-bcm2711-rpi-4-ext4-factory.img.gz

Step 8.3.2 : How to extract full image file

• To extract image file command and pathis below

• Make sure the current directory “openwrt”

$HOME/openwrt/bin/targets/bcm27xx/bcm2711

$ ls -l

-rw-r--r-- 1 sysadmin sysadmin     1685 Jan  6 01:04 config.buildinfo
-rw-r--r-- 1 sysadmin sysadmin       71 Jan  6 01:04 feeds.buildinfo
-rw-r--r-- 1 sysadmin sysadmin 17118352 Jan  6 01:05 openwrt-bcm27xx-bcm2711-rpi-4-ext4-factory.img.gz
-rw-r--r-- 1 sysadmin sysadmin 17119199 Jan  6 01:05 openwrt-bcm27xx-bcm2711-rpi-4-ext4-sysupgrade.img.gz
-rw-r--r-- 1 sysadmin sysadmin     4231 Jan  6 01:05 openwrt-bcm27xx-bcm2711-rpi-4.manifest
-rw-r--r-- 1 sysadmin sysadmin 15352083 Jan  6 01:05 openwrt-bcm27xx-bcm2711-rpi-4-squashfs-factory.img.gz
-rw-r--r-- 1 sysadmin sysadmin 15352930 Jan  6 01:05 openwrt-bcm27xx-bcm2711-rpi-4-squashfs-sysupgrade.img.gz
drwxr-xr-x 2 sysadmin sysadmin     4096 Jan  6 01:05 packages
-rw-r--r-- 1 sysadmin sysadmin     2141 Jan  6 01:06 profiles.json
-rw-r--r-- 1 sysadmin sysadmin      912 Jan  6 01:06 sha256sums
-rw-r--r-- 1 sysadmin sysadmin       18 Jan  6 01:04 version.buildinfo

• Command to extract full image file

$ gunzip -d openwrt-bcm27xx-bcm2711-rpi-4-ext4-factory.img.gz

• After extracting image file check with ls command it will display below file

$ ls -l

 -rw-r--r-- 1 sysadmin sysadmin 184549376 Jan  6 01:05 openwrt-bcm27xx-bcm2711-rpi-4-ext4-factory.img

Step 8.3.3: Check the content of image file

• Content of full image file

Step 8.3.4 : Check the size of the full image

• The du (disk usage) that allows users to analyze and report on disk usage within directories and files.

• Displays sizes in human-readable format, using units such as KB, MB, GB, etc.

  $ du -h openwrt-bcm27xx-bcm2711-rpi-4-ext4-factory.img.gz
  
  17M     openwrt-bcm27xx-bcm2711-rpi-4-ext4-factory.img.gz
  

• As we can see size of image file is around 17M